Surgical approaches are the dominant correction for spinal deformities, in particular those associated with scoliosis. Scoliosis is a progressive condition normally affecting young women during their skeletal development. In the US it is common for all 5th grade children to be assessed for any spinal deformation. Progression from a slight spinal angle, referred to as the Cobb angle 101, to a large deformation >35 degrees 102 can occur rapidly (FIGS. 1A-1B). Significant health conditions can occur with angles greater than 70 degrees, including respiratory, neurological, and social health issues associated with the cosmetic aspects of the deformity.
Surgical approaches began in the mid-20th century and remain substantial and invasive. The initial approach involved the surgical introduction of Harrington rods anchored to hooks 201 above and below the curvature of the spine to distract the vertebrae into a more anatomically correct orientation (FIGS. 2A-2B).
Implant designs evolved and now the introduction of pedicle screws 301 in multiple vertebral bodies including those involved in the curve and then attachment of the pedicle screws to rods 302 is most common (FIGS. 3A-3D).
External approaches are effective at reducing the progression of the deformity as measured by the Cobb angle. A recent publication of a prospective randomized trial of 242 patients of the use of an external brace vs. no brace was published in the New England Journal of Medicine [NEJM, 2013 Oct. 17; 369(16):1512-21].
The study methodology included patients with Cobb angles between 20 to 40 degrees and having not developed to skeletal maturity. Effectiveness of the brace was defined as attainment of skeletal maturity without progression to 50 degrees or more of curvature, which signaled treatment success.
Braces incorporate the mechanical principles of three-point bending into their designs, where three forces are applied to an object in a direction that would tend to bend the object (FIG. 4).
A moment's effectiveness depends on its distance from the opposing force, also called the moment arm. It takes more force to close a heavy door if you push very close to the hinge than if you push on a doorknob near the edge. Translated, the applied rotational moment increases because the moment arm increases.
Designers of orthoses incorporating three- and four-point force or pressure systems seek to maximize moment arms within anatomical boundaries to achieve the largest bending moment on the spine with the smallest possible forces.
These braces provide 3-point leverage to bony anatomy about the spine (FIGS. 5A and 5B). The rib cage and the pelvis being the major bony groups which provide rigid purchase for the braces. These braces produce static pressure and are worn for hours throughout the day and night. A clear finding from the randomized study was that there was a significant positive association between hours of brace wear and rate of treatment success with >90% of patients that wore the braces for greater than 12.9 hours (FIG. 6).
In a subsequent comment also published within the NEJM, an equally important finding of this study was that so many growing children with adolescent idiopathic scoliosis “seem to do just fine with no treatment at all,” said Dr. Eugene J. Carragee and Dr. Ronald A. Lehman Jr., “the bracing indications described are probably too broad, resulting in what may be unnecessary treatment for many patients,” Dr. Carragee and Dr. Lehman said. Although there do not appear to be physiological side effects to bracing in adolescent idiopathic scoliosis, “it carries financial, emotional, and social burdens that need to be considered.” They also cited that 48% of the untreated patients had a successful outcome, as did 41% of the patients with braces.
Since these patients are predominantly school-aged girls and compliance is directly correlated to outcome therein lies the clinical need for shorter duration, effective therapy that can equal or surpass these results of these present braces. Some braces try to address this by prescribing them to only be worn at night, such as the Charleston Bending Brace, which has an added benefit of being engaged while the muscles surrounding the spine are relaxed and attempts to provide a correcting force (Clin et al., Spine 2010 Sep. 1; 35(19):E940-7). The paraspinal muscles are engaged while standing and relax when lying down. The philosophy for this brace includes the supposition of biomechanical advantage that wearing a brace while these muscles are relaxed can produce an equivalent benefit in shorter duration than the upright day time braces. To date while there have been no randomized studies to confirm the clinical performance of these braces to one another, observational studies show similar results from long hours in a day time brace when compared to shorter hours in night time braces.
While the surgical approach is an option in the United States, the waiting list in other countries with socialized medicine can be as long as 18 months. In these countries and communities, a non-surgical option may be a valuable medical and economic alternative to not only limit Cobb and progression but potentially reverse its course.